Easily-openable, hermetically-sealed, packaging bag

Abstract: An easily-openable, hermetically-sealed, packaging bag 1 whose opening end is heat-sealed, with a sealing material interposed therein, wherein the sealing material comprises (a) an intermediate resin strip comprising a low-sealable resin layer and (b) two outer resin strips, the outsides of the outer resin strips being strongly bonded to the inside of the packaging bag by heat-sealing and being weakly melt-bonded to both sides of the intermediate resin strip, the innermost ends of the melt-bonded interfaces between the intermediate resin strip and the outer resin strips are located inner in the packaging bag than the innermost ends of the heat-sealed parts between the packaging bag and the outer resin strips.

Description: BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to easily-openable, hermetically-sealed, packaging bags which are suitable for packaging boil-in-pouch foods or retort-in-pouch foods. (b) Description of the Related Art Hermetically-sealed bags are usually produced by filling a packaging bag with a content through an open end, closing the open end to make contact between two opposite sides of the inside of the packaging bag and then heat-sealing the opposite sides to each other. The thus produced hermetically-sealed packaging bags are unsatisfactory because when the sealability is increased by increasing the heat-sealing strength, the opening step is made difficult, requiring cutlery for opening to use the contents. Particularly, packaging bags to be subjected to heat processing, such as retort sterilization, need such a high sealability as to stand the internal pressure increased by the heat processing, and are difficult to endow with good opening characteristics. A means proposed to solve this problem is to heat-seal with relatively low heat-sealing temperature the inside of the open end of packaging bags, with a sealing material, which is composed of two strips being bonded to each other with an adhesive which can make a good seal with the inside of the packaging bags, interposed in the open end, to give a hermetically-sealed packaging bag, which has a high sealability and also has good opening characteristics ensured by the peeling between the surfaces bonded by the adhesive. This means however is poor in the productivity because of the complicated procedures for applying adhesives. SUMMARY OF THE INVENTION The object of the present invention is to provide an easily-openable, hermetically-sealed, packaging bag which exhibits both good opening characteristics and high sealability without the aid of adhesives. The inventors made researches to solve the above-described problems and found that easily-openable, hermetically-sealed, packaging bags being excellent both in sealability and in opening characteristics are obtainable by heat-sealing the inside of the opening end of packaging bags, with a layered sealing material of a specific layer structure interposed therein. Based on the finding, the inventors have completed the present invention. That is, the present invention provides an easyly openable, hermetically-sealed, packaging bag, comprising a packaging bag and a sealing material of a strip form, the packaging bag having an opening end which is hermetically sealed, with the sealing material interposed therein, and with the inside of the opening end strongly bonded to both sides of the sealing material by heat-sealing to form two strongly heat-sealed parts between the inside of the packaging bag and both sides of the sealing material, characterized in that the sealing material comprises (a) an intermediate resin strip comprising a resin layer having low sealability which is hard to bond to the inside of the packaging bag by heat-sealing and two resin layers which are strongly melt-bonded to both sides of the low-sealable resin layer to form two strongly melt-bonded interfaces and (b) two outer resin strips which are weakly melt-bonded, respectively, to both sides of the intermediate resin strip to form two weakly melt-bonded interfaces between the intermediate resin strip, and the outer resin strips, the innermost ends of the weakly melt-bonded interfaces being at a more inner location in the packaging bag than the strongly heat-sealed parts. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially sectional view of the easily-openable, hermetically-sealed, packaging bag according to the present invention, illustrating the parts for opening. Fig. 2 is a partially sectional view of another embodiment of the easily-openable, hermetically-sealed, packaging bag according to the present invention, illustrating the parts for opening. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail referring to drawings. Fig. 1 is a partially sectional view of an embodiment of the easily-openable, hermetically-sealed, packaging bag according to the present invention, illustrating the structure of the opening end of the packaging bag. The referential numeral 1 represents a packaging bag which is made of synthetic resin and is composed of a single layer strip or a multilayer strip, for example, of a polyethylene, a polypropylene, a polyester, a polyamide or a polyvinylchloride. In case of a packaging bag composed of a multilayer sheet, the outer layer (to come contact with sealing bars 11) of the multilayer sheet preferably has a higher melting point than that of the inner layer (to be used for sealing). An example of the preferred combination of the resins is a combination of an oriented nylon for the outer layer and a polypropylene for the inner layer. The referential numeral 2 represents an intermediate resin strip, composed of a low-sealable resin layer 3 and two resin layers 4 and 5 sandwiching the low-sealable resin layer 3. The low-sealable resin layer 3 is strongly melt-bonded to the resin layers 4 and 5. The peeling strength between the low-sealable resin layer 3 and the resin layers 4 and 5 is preferably 6 to 8 kg/15 mm. The low-sealable resin layer 3 and the resin layers 4 and 5 may be made of the same resin, and also may be previously united in one body. The resin layers 4 and 5 of the intermediate resin strip 2 is weakly melt-bonded to the outer resin strips 6 and 7 on two melt-bonded interfaces 8. The outside of each of the outer resin strips 6 and 7 is strongly bonded to the inside of the packaging bag 1 at two heat-sealed parts 9. The peeling strength of the melt-bonded interfaces 8 is preferably 300 to 1,500 g/15 mm. The outside of each of the outer resin strips 6 and 7 is strongly bonded by heat-sealing to the inside of the packaging bag 1 at two heat-sealed parts 9. The peeling strength of the heat-sealed parts 8 is preferably 6 to 8 kg/15 mm. In the case where the inner layer of the packaging bag 1 is a polypropylene layer, the low-sealable resin layer 3 is preferably a layer of a linear low density polyethylene, and the outer resin strips 6 and 7 are preferably strips of a polypropylene. The outer resin strips 6 and 7 also may be of different resins so that one of the melt-bonded interfaces 8 is easily peelable and the other is hard to peel. The sealing material shown in Fig. 1 may be a three-layer strip produced by three-layer extrusion. When the easily-openable, hermetically-sealed, packaging bag 1 as shown in Fig. 1 is opened, easy open is attained by the peeling on one of the melt-bonded interfaces 8. In this embodiment, the outermost end of the low-sealable resin layer 3 of the intermediate resin strip 2 is located outer toward the outside of the packaging bag 1 than the outermost ends of the outer resin strips 6 and 7, so that opening is performed easily by the concentration of the applied stress at one of the outermost ends of the melt-bonded interfaces 8, and so that the opposite sides of inside of the packaging bag 1 are prevented from bonding to each other and making opening difficult. The distance between the outermost end of the low-sealable resin layer 3 and the outermost ends of the outer resin strips 6 and 7, namely t 1 in Fig. 1 may be 0 mm, but preferably be at least 0.5 mm, more preferably 5 to 30 mm. Further, since the innermost ends b of the melt-bonded interfaces 8 between the intermediate resin strip 2 (outer resin layers 4 and 5) and the outer resin strips 6 and 7 are located inner in the packaging bag 1 than the innermost ends 10 of the heat-sealed parts 9 between the packaging bag 1 and the sealing material, the internal pressure can be concentrated at the innermost ends 10 of the parts strongly bonded by heat-sealing while the hermetical sealing is maintained, to give good sealability against internal pressure. The preferred distance t 2 as shown in Fig. 1 between b, namely the innermost ends b of the melt-bonded interfaces 8 between the intermediate resin strip 2 and the outer resin strips 6 and 7, and 10, namely the innermost ends of the heat-sealed parts 9 between the packaging bag 1 and the sealing material, is generally at least 0.5 mm, more preferably 5 to 30 mm. The intermediate resin strip 2 as shown in Fig. 1 has a multilayer structure wherein the innermost ends of the resin layers 5 and 6 are arranged inner in the packaging bag 1 than the innermost end of the low-sealable resin layer 3 by a distance t 3 , and such an intermediate resin strip can further improve the sealability of the packaging bag 1, as compared with an intermediate resin strip with an even innermost end line. The preferred distance T 3 is generally at least 0.5 mm, more preferably 5 to 30 mm. The easily-openable, hermetically-sealed, packaging bag of the present invention as shown in Fig. 2 is provided with a fastening tape 12 inside the opening end and outer than the sealing area, to give a retort pouch which can be opened and sealed repeatedly. The easily-openable, hermetically-sealed, packaging bag of the present invention is obtainable by filling a packaging bag made of a synthetic resin with a content through an opening end, closing the opening end so that the inside of the packaging bag consists of two sides opposing to each other, with a sealing material or the strip materials constructing the sealing material interposed in the opening end, and then bonding the inside of the packaging bag to the both sides of the sealing material by heat-sealing. Herein heat-sealing means various heat-sealing techniques using thermal energy, such as heat-sealing using an ordinary heat-sealer using heat and pressure, impulse heat-sealer, high-frequency dielectric sealer or ultrasonic sealer. The melt-bonding between the layers in the sealing material may be performed at the time of heat-sealing the packaging bag with sealing bars 11, with the strip materials constructing the sealing materials interposed in the predetermined positions, or may be performed previous to the heat-sealing of the packaging bag, or may be partially performed before the sealing material is interposed in the packaging bag and then be completed at the time of the heat-sealing. To attain stably good opening performance, it is preferable to use, as parts of the sealing material, multilayer strips weakly melt-bonded (for example, a multilayer strip consisting of the layers 4 and 6 and a multilayer strip consisting of the layers 5 and 7). Some examples of the resin combinations in such multi layer strips include a combination of a polypropylene and a linear low density polyethylene and a combination of a polypropylene and a mixture of a polybutene-1 and an ethylene-vinyl acetate copolymer. Each of the multilayer strips is preferably so arranged in the packaging bag so that a resin layer of a higher melting point is located at the outermost side of the sealing material. Hereinafter the present invention will be described in detail referring to the following Examples, which however do not limit the scope of the present invention. EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 AND 2 As shown in Fig. 1, the opening end of each packaging bag 1 made of a two layer strip of the layer structure as listed in Table 1 was closed so that the inside of the packaging bag consists of two sides opposing to each other, with a sealing material having the layer structure as listed in Table 1 interposed in the open end, and then the packaging bag 1 was so sealed by heat-sealing the opening end under the conditions as listed in Table 1 at a sealing width of 5 mm and at a sealing pressure of 4x10 2 mPa (4 kgf/cm 2 ) as to give the distances t 1 and t 2 as listed in Table 1. At the time of interposing the sealing material, two-layered strips (a strip consisting of layers 6 and 4 and a strip of layers 5 and 7) each of which had previously been melt extruded were placed on both sides of a low-sealable resin layer 3. The sealed packaging bags were opened and the results are listed in Table 1. In Table 1, ONY represents an oriented nylon, CPP a polypropylene, LLDPE a linear low density polyethylene, PB-1 a polybutene-1 and EVA an ethylene-vinyl acetate copolymer. E.O. means easy open with an opening force of 9.8 N/15 mm (1 kgf/15 mm) width or lower, E.O.(-) means easy open with an opening force of 12.7 N/15mm (1.3 kgf/15 mm) width or lower, and T.S. means tight seal or the break of film.

Claims: An easily-openable, hermetically-sealed, packaging bag, comprising a packaging bag (1) and a sealing material of a strip form, the packaging bag having an opening end which is hermetically sealed, with the sealing material interposed therein, and with the inside of the opening end strongly bonded to both sides of the sealing material by heat-sealing to form two strongly heat-sealed parts (9) between the inside of the packaging bag (1) and both sides of the sealing material, characterized in that the sealing material comprises (a) an intermediate resin strip (2) comprising a resin layer (3) having low sealability which is hard to bond to the inside of the packaging bag (1) by heat-sealing and two resin layers (4) and (5) which are strongly melt-bonded to both sides of the low-sealable resin layer (3) to form two strongly melt-bonded interfaces (9) and (b) two outer resin strips (6) and (7) which are weakly melt-bonded, respectively, to both sides of the intermediate resin strip (2) to form two weakly melt-bonded interfaces (8) between the intermediate resin strip (2), and the outer resin strips (6) and (7), the innermost ends of the weakly melt-bonded interfaces (8) being at a more inner location in the packaging bag (1) than the strongly heat-sealed parts (9). The easily-openable, hermetically-sealed, packaging bag of claim 1, wherein the outermost end of the resin layer (3) having low sealability of the intermediate resin strip (2) is located outer toward outside of the packaging bag (1) than the outermost ends of the outer resin strips (6) and (7). The easily-openable, hermetically-sealed, packaging bag of claim 2, wherein the intermediate resin strip (2) consists of the resin layer (3) having low sealability and two resin layers (4) and (5) which are strongly melt-bonded to both sides of the low-sealable resin layer (3), respectively, and the outermost end of the melt-bonded resin layer (3) is located outer toward outside of the packaging bag (1) than the outermost ends of the resin layers (4) and (5) and the outermost ends of the outer resin strips (6) and (7). The easily-openable, hermetically-sealed, packaging bag of claim 3, wherein the packaging bag (1) is made of a multilayer sheet comprising at least an inner layer of a synthetic resin and an outer layer of a synthetic resin, the synthetic resin of the outer layer being higher in melting point than the synthetic resin of the inner layer. The easily-openable, hermetically-sealed, packaging bag of claim 4, wherein the outer layer of the packaging bag (1) is an oriented nylon layer, the inner layer of the packaging bag (1) is a layer of a polypropylene, each of the outer resin strips (6) and (7) is a strip of a polypropylene, each of the resin layers (4) and (5) is a layer of a linear low density polyethylene or a mixture of a polybutene-1 and an ethylene-vinyl acetate copolymer, and the resin layer (3) having low sealability is a layer of a linear low density polyethylene.

Inventors: GOTOH SHUICHI, ODAKA HIROSHI, GOTOH, SHUICHI, ODAKA, HIROSHI, GOTOH, SHUICHI, C/O IDEMITSU PETROCHEM. CO., LTD., ODAKA, HIROSHI, C/O IDEMITSU PETROCHEM. CO., LTD.
Applicants: IDEMITSU PETROCHEMICAL CO, IDEMITSU PETROCHEMICAL CO., LTD.
Application year: 1994
Main classification: B65D75
IPC codes: B65D33, B65D75, B65D77